<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <button>西八</button>

    <script>



        window.addEventListener('load', function () {
            var btn = document.querySelector('button');
            btn.addEventListener('DOMcontentLoaded', function () {
                
            })
            alert('你长的真好看啊');
        })
    </script>
</body>

</html>